Manufacture of purified cellulose material from hemp fibers



Patented Feb. 28, 1933 UNITED STATES PATENT OFFICE- EDWARD GHLAUNCEY WORDEN, 151, OF MILLBURN, NEW JERSEY, ASSIGNOR TO ,HANSON & ORTH, OF NEW YORK, N. Y., A FIRM COMPRISING CHARLES D. ORTH, SR., MICHAEL 3'. SMITH, AND CHARLES D. ORTH, JR.

MANUFACTURE OF PURIFIED CELLULOSE MATERIAL FROM HEMP FIBERS No Drawing.

This application is a continuation in part of application Serial No. 347 ,7 28, filed March 16, 1929, issued as Patent 1,866,917, dated July 12, 1932, for Manufacture of cellulose material from hemp fiber designated by the commercial name of Manilos, and'relates primarily to the industrial treatment and utilization for the production of purified cellulose of the fibers, of various kinds, species or grade's'of hemp, said cellulose in the purified state, and of composition as herein specified, having been found highly advantageous for use in the arts, as in the manufacture of rayon, as more specifically set forth in my co-pending application, Serial No. 347,457, filed March 15, 1929, for Manufacture of rayon from hemp fiber, the product being designated by the commercial name of Maniray. By rayon or artificial filaments is understood to comprise those esters and ethers of cellulose, which, after being placed in solution, are afterwards forced through orifices of various shapes and sizes into a liquid or other medium whereby they are changed from a liquid to a solid form with or without decomposition being sometimes precipitated as a hydrated cellulose with decomposition of the cellulose compound or cellulose ester or ether, or deposited as the cellulose ester or ether by the volatilizatiorr of the solvent portion. In the first group would be included rayon produced from viscose and cupra-ammonium cellulose solutions. From the second group, would be included the nitrocellulose filaments which are afterwards denitrated, the organic esters of cellulose such as acetated cellulose, and the alkyl-, aryl and aralkyl-eelluloses, typified by the ethyl celluloses, benzyl celluloses, and ethylbenzyl celluloses.

There appears to be and to have been a looseness in the use of the Word hemp by some writers. Hemp in this invention is to be understoodas covering and including the hemp fibers, as stated on page 190 of Report No. 9, U. S. Department of Agriculture, A

Descriptive Catalogue of Useful Fiber Plants of the World, by Charles Richards Dodge, published at the Government Printing Office, Washington, D. C. 1897. Of these hemp 1929. Serial N0. 356,890.

fibers therein listed, I have obtained especially useful purified cellulosic fibers for the manufacture of esters and ethers, for theproduc: tion of rayon artificial filaments and for other uses, by the employment of fibers and other components of and obtained from thebotanical genus or group Musa, of which M usa tea"- tz'lz's and Musasapz'entum are perhaps most well known. My researches upon the use in this connection of the fibers of the Sanseoiem'a and Yucca, in the main, have been less satisfactory. Hemp fibers in general, when in the partially purified state, whether that purification be mechanical, chemical or both, are distinguished by their relatively great tensile strength, and also by their resistance to chemical treatment with the minimum of degradation, depolymerization or hydrolysis of the cellulose or cellulose aggregates contained therein, and hence with the minimum in diminution of tensile strength both of the individual fiber and in the aggregate. Furthermore, this tensile strengthappears to be intimately associated with the length of the in dividual fiber or cell, and admits of purification for the formation therefrom and separation of a cellulose or cellulosic material relatively high in alphacellulose or resistantcellulose and containing but relatively small amounts of hemicelluloses and other inferior celluloses or cellulose-like bodies. This high alpha-cellulose content, absence of notable amounts of inferior celluloses, coupled with unusual length of fiber, renders hemp cellulose purified as described herein peculiarly adapted for esterification and etherification purposes and for the formation of high strength artificial filaments, provided the series of treatments or steps to which the cellu losic material is subjected in transformation from purified cellulose to artificial filaments procedure of esterification, the initial length and strength of the cellulose fiber to be esterfied apparently bears a definite relation to the strength of the esterified cellulose made therefrom, and this relationship of strength and tenacity is especially exemplified when the esterized cellulose is dissolved and placed in filament or film form from an evaporation therefrom of the volatile solvent or solvent combination contained therein. In other words, where the tensile strength and length of fiber of the initial purified cellulose is relatively high, other conditions of treatment being the same, the esterified product will be correspondingly high in tensile strength and other desirable characteristics. That is, these desirable constants are found to augment with an increase in strength of the original cellulose from which compounds are produced by the esterifying or other process or processes to which the cellulosicfibers are subjected, and that the stronger the original purified cellulosic fiber, other conditions remaining substantially the same, the stronger will films and filaments be when the cellulose is transformed into ester form, dissolved, and deposited either as a film by the removal of solvent, or as a filament by the same procedure, or by precipitation, setting, coagulation, de-' composition or otherwise.

That is, a relativelylong fiber cotton upon proper nitration, for example, will produce a cellulose ester, which when dissolved and the solvent removed therefrom, forms a film or' filament of greater tensile strength and other desirable physical qualities than will a rela tively much shorter cotton fiber (such as linters or fly), when treated in the same manner.

This desirable difference has been found to be due in a large measure to the greater length and strength of the individual cellulose cell in the longer fiber cotton. This generalization has been substantiated in the organic cellulose ester art as in cellulose acetate manufacture and insofar as I am aware, also in the relatively newer and less comprehensively explored cellulose ether art.

Furthermore, in the production of those cellulose esters represented by the xanthated cellulose (viscose) it has been noted that the relatively shorter wood cellulose fibers do not admit of theproduction of a rayon filament of as high tensile strength and other desirable physical characteristics as when the relatively longer cotton cellulose fibersin their purified state have been submitted to the same steps of treatment under comparable conditions, and cotton celulose fiber is being admixed with wood cellulose fiber in large quantities at the present time for viscose rayon manufacture,

in order to increase the tensile strength both in the wet and dry state and other qualities of the individual fibers and fiber aggregates, over that which would normally result if wood cellulose alone be used.

There appears to be a well defined relationship between the length and strength of the original cellulose fiber used for esterification and etherification purposes-and the tensile strength and other qualities of filaments and films producible therefrom, irrespective of whether the final product is the cellulose ester or ether in the solid form or whether the final product is a de-esterified filament or film as in viscose and nitrocellulose rayon.

It is conceded that hemp fiber possesses unusual strength when compared with 'wood fiber or cotton cellulose fiber, all preferably being in the purified state. These two constitute the two kinds of cellulose fibers used commercially for the purpose at the present time.

coincidental with an increase in tensile strength of initial purified cellulosic fiber as used for esterification purposes, usually comes a diminished reactivity, especially to chemical reagents, and corresponding adjustments of factors of concentration, avidity of reactiveness, time factor, temperature, pressure, etc.

are usually necessary due to this property,-

when operating upon celluloses from various origins and in different degrees of purity, depending in a measure upon-the nature and amount present of associated bodies. commercial recognition of the pertinency of The.

these observations is apparent at the present time, in endeavors to supplant a portion of the wood cellulose heretofore used in viscose rayon production, with an equivalent amount for rayon production, and corresponding variations and adjustment in chemicals, concentration, time, temperature and similar factors are required in order to purify and esterify under optimum conditions as to yield and quality of resultant product obtained.

This generalization holds true likewise, in the manufacture of cellulose ester and ether filaments, especially to viscose rayon filaments from highly purified cellulose from hemp over both that of purified cellulose as.

obtained from wood and from cotton, and departure from the standard procedure for alkali cellulose formation and subsequent xantha-tion with the intermediate steps is necessary to obtain highly desirable results, and in order to induce optimum conditions in the various phases of treatment from initial cellulosic material to finished product, whether that product be an ether, ester, or an ester which has been partially or entirely de-esterified or otherwise modified usually with the formation of hydrated or regenerated cellulose.

This invention, therefore, is primarily concerned with the respective steps in treatment of the fibers commercially classified under the general heading of hemp as heretofore indicated, for the preparation therefrom of a cellulosic material high in alphacellulose, and relatively low in hemicellulose and other inferior cellulosic bodies, and admirably adapted for the transformation into rayons and other artificial filaments, films, etc. on account of its high alphacellulose or resistant cellulose fonated corn oil, etc.).

have been obtained by the omission of alkali content, and b virtue of the practical absence. of interior cel uloses and cellulosic bodies.

In the illustrative example to follow, it is to be understood that the method of procedure will necessarily Vary, as well as the amounts and nature of chemicals used, time, and variations in temperature, pressure and concentration factors, depending in a large measure upon the nature and source from which the hemp was obtained, whether from the male or female plant, and the physical condition as to disintegration of the fibers or bundles of fibers, at the time of the treatment of purification preliminary to esterification is commenced.

It is usually immaterial whether the hemp has been submitted to a previous retting or similar operation, has been scutched or heckled, or a combination of two or more of these or other operations has been applied to Bacteriology and mycology plays an important role, in the connection. I prefer as the first chemical operation (the fiber previously having been placed in physical condition to make it of proper receptivity to chemical treatment) to boil the fibers or fiber bundles or aggregates with an excess of water containing 3%10% free alkali metal hydroxide, O.5%8% alkali metal silicate and 0.5 Zn-4% corn oil or other readily saponifiable or sulfonated vegetable or animal oil or mixtures thereof, or an equivalent amount of the oil or sulfonated oil already saponified. Satisfactory results have also been obtained by substituting for the saponified oil, the alkali metal salts of the sulfonated oils (i. e. Turkey red oil, alizarin assistant, saponified sul- Satisfactory results metal silicate solution, and proportion and nature of chemicals used may be modified, diminished or increased by varying time and pressure factors in subjecting the fibers to heating, the chemicals, heat and time being so adjusted and controlled as to insure a maximum of purification with a minimum reduction in tensile strength, quality and desirability for esterification purposes of the treated cellulose-containing material. The alkali metal silicate in some cases may advantageously be substituted by the alkali metal carbonates, bicarbonates or sesqui-carbonates. The fiber is placed in a pressure kier, and submitted to heat, preferably at a temperature of around 110 C., circulation being aided, if desired, by means of a circulatory arrangement for pumping continuously the boil-off liquor over the mass of fibers. It has been found that the addition to the boil-ofi' liquor of an amount of soluble water glass is espe-' cially beneficial in scouring and removal of intercellular and cementitous material, fats, oil, wax and similar encrusting and adhering impurities, and tends to leave the fiber in an especially porous and absorptive conditon for quick and complete penetration of reagents used in normal esterifying and etherifying processes. The boil-ofi operation is continued from 3 to 8 hours depending upon the comparative amounts of naturally occurring organic silicon compounds and impurities in the fibers or fibrous aggregates, after which the boil-off liquor is allowed to drain off, and clear water added, and heat applied, and this alternate addition of water, heating, and discarding of the wash water is continued until the wash waters are practically colorless, and a sample of material when extracted in a Soxhlet or other suitable apparatus with a chemical such as ether, gives practically no extractive and an ash determination has shown the inorganic residue to be reduced to a minimum.

The fibers, still in the wet condition, are preferably passed through friction rollers which tend to break down and disintegrate the fibrous bundles or masses, the fibers being subjected to a running water washing treatment in an elutriating manner, whereby intercellular and encrusting material is disintegrated, and is removed in and by the wash water. The fibres may then be hydroextracted, and submitted to an electrolytic (preferably) chlorine bleach, care being taken that the fibers are not exposed to the atmosphere during the bleaching and subse quent acidifying operation, to minimize formation of oxycellulose and other oxidation celullosic compounds, deleterious from the viewpoint of the use of the purified hemp fiber for purposes of ether and ester formation.

The fibers of a degree of whiteness depending upon the thoroughness of the preliminary treatment and the factors of time and chemical concentration in the bleaching operation are now washed until all but traces of reactants are removed, and dried at a comparatively low temperature. For ease in'manipulation during esterification, and the steps preceding and suceeding it, it is advisable to make the fibers into sheet paper, either along or with admixture thereto of other celluloses suitable for esterification treatment, such as wood pulp cellulose, cotton, linters, and the like, the proportions used, depending upon the final results desired, and the details of 5 treatment to which the cellulosic material is to be subjected.

On account of the much greater contractility and reduction in superficial area of sheets of cotton or hemp celluloses over wood 19 cellulose when subjected to sodium hydroxide treatment in alkali cellulose formation preliminary to xanthation in viscose rayon manufacture, I prefer to admix the proportion of hemp cellulose with other cellulose or celluloses preliminary to sheet formation.

One or more of the foregoing steps may be prolonged, shortened, repeated or otherwise modified, depending upon the comparative resistivity or refractoriness of the hemp fiber to be purified, or the concentration of'the baths may be increased'or diminished, as conditions may arise.

The purified hemp cellulose, as the mean of determinations of several lots, gave figures as follows Maximum Minimum Mean Per cent Per cent Per cent The absorption of the cellulose is shown by the fact that a pledget of the same placed upon the surface of water at room temperature will be immersed by its own weight, usually in less than 30 seconds. Alphacellulose determinations made on various samples indicated that it was usually practically pure alphaor resistance cellulose, and with but negligible amounts of other cellulosic materials present, while the original tensile strength of the fiber was substantially conserved. In what is regarded as an especially suitable purified hemp cellulose, for esterification purposes, the following were the constants obtained from an air-dry sample The determinations were calculated from the sample in the moisture free state.

The color of the purified individual fibers varies from a light straw color to pure white,

depending upon the thoroughness and care' exercised inthe purification treatments. Inasmuch, however, as rayon filaments are usually bleached, I prefer to submit the cellulose to what is known in the trade as between a three-quarters and full bleach, in order to conserve to the maximum, the tensile strength of the individual cellulosic fibers. Excessive bleaching diminishes the tensile strength and desirability of the fiber for the purposes intended.

Nitration experiments conducted under varying conditions as to time, temperature and relative proportions of water, nitric and sulfuric acids in the esterizing mixture as compared with simultaneously conducted control esterifications with cotton and with wood celluloses, demonstrated superiority of purified hemp cellulose, for fluid and solid nitrocelluloses. The viscosity of nitrated hemp cellulose is usually greater than an equal weight of nitrated wood, wood or cotton celluloses when dissolved in the same solvent or solvent combinations. N itrated hemp celluloses possess a high thermoplasticity when admixed with camphor and other flexilizers, extensibility-producers and plasticizing agents, and are soluble in acetone, alkyl acetates, diacetone alcohol, and softened by the dihydroxyand trihydroxy-aliphatic and carbocyclic esters, such as glycol diacetate and resorcinol triacetate. In the production of acetated cellulose from hemp cellulose, the initial acetation progresses more slowly in general, higher temperatures and a larger proportion of energetic catalyst may be used with a minimum of cellulosic degradation, and partial hydration subsequent to acetation requires a longer time to reach the point of solubility represented by complete solution in pure acetone and incipient plasticity and gelatinization in alcohol free chloroform.

The solubility in degree and range of solvents is about the same as with acetated cotton cellulose, but dissolution usually proceeds with less facility. The same generalizations have been found to hold true in the formation of acetated celluloses, and appears to be the same in cellulose ether technology.

I am aware that it is proposed to produce paper from hemp fibers by the addition thereto in a partially purified state of varying amounts of filling and loading materials, sizes, albuminous and other organic inorganic productsto induce specific surface and interior eflects in the paper so produced. I lay no claim to this.

But what I do claim and desire to secure by Letters Patent is:

1. A process for the production of highly purified alpha-cellulose from Musa fiber con-' prising mechanically disintegrating then heating said fiber in an aqueous solution of 3%10% sodium hydroxide, 0.5%8% sodium silicate, and a sulfonated oil until the hemicellulosic and non-resistant cellulosic bodies have been softened and are in condition for removal by washing, lixiviating the mass until products of reaction are removed therefrom decolorizing the resulting purified cellulosic portion with chlorine in the absence of air, washing until neutral, substantially as herein set forth.

2. A process for the production of highly purified alpha-cellulose from M use fiber comprising mechanically disintegrating then heating said fiber in an aqueous solution of 3%10% sodium hydroxide, 0.5%8% sodium silicate, and a sulfonated oil until the hemicellulosic and non-resistant cellulosic bodies have been softened and are in condition for removal by washing, lixiviating the mass until products of reaction are removed therefrom and drying at low temperature substantially as herein set forth.

3. A process for the production of highly purified alpha-cellulose from Musa fiber comprising mechanically disintegrating then heating said fiber in an aqueous solution of 3%-10% sodium hydroxide, 0.5%8% sodium silicate, and an alkali salt of sulfoncated oil until the hemi-cellulosic and nonresistant cellulosic bodies have been softened and are in condition for removal by washing, lixiviating the mass until products of reaction are removed therefrom decolorizing the resulting purified cellulosic portion with chlorine in the absence of air, washing until neutral, substantially as herein set forth.

4. A process for the production of highly purified alpha-cellulose from Musa fiber comprising mechanically disintegrating then heating said fiber in an aqueous solution of 3 %10% sodium hydroxide, 0.5%8% sodium silicate, and 0.5%4% of the sodium salt of a sulfonated vegetable oil until the hemicellulosic and non-resistant cellulosic bodies have been softened and are in condition for removal by washing, lixiviating the mass until products of reaction are removed therefrom decolorizing the resulting purified cellulosic portion with chlorine in the absence of air, washing until neutral, substantially as herein set forth.

In witness whereof I attach my signature hereto.

EDWARD CHAUNCEY WORDEN, 1st. 

